1. Field of the Invention
The present invention relates to a stylet unit of the type having a flexible, tubular stylet sleeve, and a flexible inner stylet wire, inserted into the stylet sleeve. At least a portion of the stylet wire and at least a portion of a channel defined by the stylet sleeve has a non-circular cross-section for preventing rotation of the wire inside the sleeve. The stylet unit also has a handle, by means of which the sleeve and the stylet are movable in relation to each other in a longitudinal direction, the sleeve and the wire being connected at one end thereof to the handle.
2. Description of the Prior Art
Stylet units of the above type are widely used for medical purposes. The wire and the sleeve are adapted to be inserted into an oblong element, normally an electrode cable of a heart stimulator that is to be introduced into a mammal body for surgical purposes. The purpose of the unit is to locate the oblong element in the body. Typically, an end of the cable is anchored in the atrium or ventricle of a patient by means of the style unit.
A stylet unit of the above general type is especially suitable for stiffening and maneuvering a hollow electrode cable for a heart stimulator, in conjunction with introduction of the electrode cable into a patient's heart, and for anchoring the contact electrode (electrode head) on the distal end of the cable in a cavity in the heart. Introduction of such an element into the heart is usually performed through a suitable vein, and the contact electrode can be anchored in the right ventricle or atrium. The stylet unit temporarily contained inside the hollow electrode cable extends through the cable's central channel from the cables proximal end (which is subsequently connected to the heart stimulator) to its distal end on which the contact electrode is located.
Especially in the anchoring of a contact electrode in the heart's atrium, a stylet unit is appropriately used with which the distal end section of the electrode cable can be given a suitable shape, simplifying the introduction of the end section into the atrial auricle and anchoring of the contact electrode in the trabeculae of the atrial auricle. After the contact electrode (that is the electrode cable) has been anchored at the desired site in the heart, the stylet unit is withdrawn from the electrode cable.
U.S. Pat. No. 5,728,148 describes and shows a stylet unit with a double stylet combination having a flexible, tubular stylet sleeve holding an inner stylet wire which is moveable in the sleeve's central channel. At the proximal end of this known stylet unit, there is an operating handle with which the sleeve and inner stylet wire can be moved in relation to each other to retract the wire's pre-bent distal end section into the distal end section outside the opening of the sleeve's end section into the central channel of the distal end section of the surrounding electrode cable, thereby imparting the desired bent shape to the end of the cable. Accordingly, a J-shaped distal end of the electrode cable, suitable for anchoring purposes, can be obtained by deploying the distal end section of the pre-bent wire into the electrode channel.
In order to prevent undesirable rotation of the stylet wire in the surrounding sleeve within at least a longitudinal section of the stylet unit, the wire and the sleeve channel having respective corresponding non-circular cross sections along at least a longitudinal section of the stylet. Normally, the non-circular sections are located at the respective distal end of the wire and sleeve. Both the wire and the sleeve are non-rotationally arranged within the handle, in order to permit the maneuvering of the distal end portion of the wire and sleeve.
However, when the handle is turned, for example in order to locate the thus J-shaped (or similarly shaped) and implanted electrode cable end for the exact positioning thereof, the stylet sleeve produces a torsional moment on the end of the wire. This is due to the non-circular sections of the wire and the sleeve still being in engagement with each other in the distal end regions thereof. The torsional moment on the wire might result in the wire being broken or damaged. Therefore, it may occur that a broken end of the wire is left in the electrode cable. Such a broken end may cause a major failure on the implantable lead system, with a detrimental result for the patient.